The invention relates to shutdown mechanisms for nuclear reactors, and in particular to poison release mechanisms for reactors of the liquid metal type.
It is known in the art of nuclear reactor control to use a multiplicity of small neutron absorbing masses, usually stainless steel spheres or the like, to rapidly shutdown (scram) the nuclear chain reaction on the occurrence of a severe accident. Because of the difficulties associated with resetting the masses after a scram, these prior art devices are usually provided in the nuclear reactor as a final safeguard against the most serious kinds of accidents, such as earthquakes or other events that might physically damage the regular shutdown system. Thus these devices have not been disclosed as having means for easily resetting the masses for renewed core operation, since it has been implicitly assumed that significant damage to the reactor has occurred, that repairs will be required, or that a prolonged testing period will be needed before operation can resume. During these prolonged outages, the prior art devices can be repaired or replaced, but they cannot be quickly reset if they scram inadvertently during normal operation or if they are actuated for test purposes. Examples of such prior art devices are described in U.S. Pat. Nos. 3,088,903 issued to A. Firth; 3,147,188 issued to R. H. Cambell; and 3,249,510 issued to A. J. Dohm, Jr. et al.